1. Field of the Invention
The present invention relates to a processing apparatus.
2. Description of the Related Art
Gases containing great quantities of fluorine atoms are used as etching gases in etching technologies in order to develop a reaction seed containing fluorine through plasma discharge or the like. As increasingly vigorous efforts have been made to protect the global environment on an international scale in recent years, global warming, in particular, is one of the most important issues to be addressed. Under these circumstances, reduction in the quantity of atmospheric emissions of fluorine compounds used in dry etching technologies in the prior art, which have long atmospheric life and high global warming coefficients, has become an urgent goal that we must achieve to prevent further global warming.
As a means for reducing the emission quantity of the processing gas containing fluorine compounds in the dry etching technologies, recycling of the processing gas, which may be achieved by circulating the processing gas inside the processing apparatus, has been proposed (hereafter, the processing gas that is circulated for this purpose is referred to as the “circulating gas”). Namely, a processing apparatus provided with a gas circulating mechanism that returns into the processing chamber at least a portion of the gas evacuated from the processing chamber by an evacuating mechanism has been proposed. By recycling the gas with such a gas circulating mechanism, both the quantity of gas emission and the quantity of gas consumption can be reduced, thereby contributing to the effort to prevent further global warming and also achieving a reduction in the cost of processing gas.
In addition, a gas supply mechanism having a showerhead structure has been proposed to supply the processing gas into the processing chamber evenly. This gas supply mechanism is often utilized in conjunction with the gas circulating mechanism described above. In other words, at least a portion of the exhaust gas evacuated from the processing chamber by the evacuating mechanism is circulated into the showerhead type gas supply mechanism and supplying the circulating gas to the workpiece inside the processing chamber in a shower, the efficiency with which the processing gas is utilized is further improved.
In a processing apparatus provided with the gas circulating mechanism and the gas supply mechanism described above, the pressure (back-pressure) on the downstream side of the evacuating mechanism must be set higher than the pressure on the upstream side of the gas supply mechanism at all times in order to circulate the processing gas with a high degree of efficiency. The rated back-pressure of a turbo pump which is normally used as the evacuating mechanism is most often 2˜3 Torr, and may be approximately 10 Torr in special cases. If the back-pressure of the turbo pump exceeds the rated back-pressure, the evacuating capability becomes greatly reduced. In addition, while the gas supply mechanism is connected to a processing gas source for supplying a processing gas (hereinafter referred to as a “primary gas”) directly into the processing chamber from the outside of the apparatus, the pressure in the primary gas piping is normally 1 atmosphere (760 Torr) or higher, and even if a flow regulating device (mass flow controller) is employed to reduce the flow rate of the primary gas and thus the pressure in the primary gas piping is reduced, the gas pressure level cannot be decreased any lower than approximately several Torr˜several tens of Torr.
As described above, while the processing apparatus in the prior art may be considered effective in reducing emission the processing gas and the quantity of processing gas consumption by recycling the processing gas, it is not equipped with a fully functioning gas circulating mechanism. Namely, when a circulating gas piping is provided between the downstream side of the evacuating mechanism sand the upstream side of the gas supply mechanism as in the processing apparatus in the prior art, a problem arises in that efficient gas circulation is not achieved since the back-pressure of the evacuating mechanism is approximately 10 Torr and the pressure on the upstream side of the gas supply mechanism can be lowered only down to several Torr˜several tens of Torr.